Polyurethane acrylate or vinyl type polymeric material for coating optical fibers based on a fluorinated diol

ABSTRACT

The invention provides a polyurethane type polymeric material for coating optical fibers, based on a fluorinated diol with formula I: 
     
       
         C n F 2n+1 —A—CH 2 OCH 2 —C (CH 2 OH) 2 —R 
       
     
     where n is 2 to 20, and A signifies —CH═CH or —CH 2 CH 2 —, and R is an alkyl group containing 1 to 4 carbon atoms. The invention also provides a fiber coated with this polymer which has been light-cured, and a fiber drawing method comprising a step of coating the fiber with a material of the invention.

BACKGROUND OF THE INVENTION

The invention relates to a polyurethane acrylate or vinyl type polymericmaterial for coating optical fibers or for an optical fiber ribbon basedon a fluorinated diol.

Optical fibers are known that comprise a double polymer coatingconstituted by a plasticized primary coating in contact with the glassfiber and surmounted by a secondary coating. That double coatingprotects the fiber from mechanical or chemical attack that may causeattenuation faults for optical transmission.

The adhesion of each coating to the intended support must be good andits physical properties must be compatible with the conditions underwhich the fibers are drawn, in particular with the draw rate and withthe final use of the fiber. The primary coating must absorb microbendingand any stresses on the glass. The secondary coating endows the fiberwith its mechanical properties.

Currently, primary and secondary coatings are polyurethane acrylate typecoatings that are light-cured by UV radiation.

European patent application EP-A-0 565 425 describes a fluorinatedpolyurethane acrylate type polymeric material for coating optical fibersbased on at least one diol, a diisocyanate, and an acrylate,characterized in that at least one of said compounds contains fluorineand at least one of said compounds contains sulfur.

That material has good mechanical characteristics, in particularimproved static fatigue strength. However, it employs asulfur-containing diol, for example, which involves high productioncosts because of the intermediate thiol preparation step that leads tothe production of by-products that must be eliminated. The problem isidentical to that of the other sulfur-containing compounds used toprepare the material described in application EP-A-0 565 425.

Thus, a material is sought that possesses the same mechanical propertiesbut which does not require the use of sulfur-containing products, inparticular sulfur-containing diols.

SUMMARY OF THE INVENTION

The invention provides a polyurethane type polymeric material forcoating optical fibers, based on at least one diol, a diisocyanate, andan ethylenically unsaturated compound, characterized in that the diol isa fluorinated diol with formula I:

C_(n)F_(2n+1)—A—CH₂OCH₂—C(CH₂OH)₂—R

where n is 2 to 20, and A signifies —CH═CH or —CH₂CH₂—, and R is analkyl group containing 1 to 4 carbon atoms.

In one embodiment, the diol is unsaturated and corresponds to formula:

C_(n)F_(2n+1)—CH═CH—CH₂OCH₂—C(CH₂OH)₂—C₂H₅

In another embodiment, the diol is saturated and corresponds to formula:

C_(n)F_(2n+1)—CH₂CH₂—CH₂OCH₂—C(CH₂OH)₂—C₂H₅

In an embodiment, in formula I, R is C₂H₅.

In an embodiment, in formula (I), n is a whole number in the range 6 to14 inclusive.

In an embodiment, in formula (I), C_(n)F_(2n+1) results from a mixtureand n is in the range 6 to 14 inclusive.

In an embodiment, in formula (I), n is in the range 6 to 8 inclusive.

In an embodiment of the material, the ethylenically unsaturated compoundis an acrylate.

The invention also provides a method of preparing the material of theinvention, comprising:

(i) a step of reacting the fluorinated diol with the diisocyanate toproduce a fluorinated diisocyanate pre-polymer;

(ii) a step of reacting the fluorinated diisocyanate pre-polymer with ahydroxyl-containing ethylenically unsaturated compound.

The invention also provides a fiber coated with at least one layer of amaterial of the invention which is light-cured; in particular, thislayer is the secondary layer.

In an embodiment, the material is light-cured in the presence of adiacrylate as a reactive diluent.

The invention also provides a method of drawing a fiber, comprisingcoating the fiber with a material of the invention, optionally mixedwith a diacrylate as a reactive diluent, and a light-curing step.

In particular, the polymeric material of the invention is free ofsulfur.

DETAILED DESCRIPTION OF THE INVENTION

The diisocyanates and the ethylenically unsaturated compounds such asvinyl ethers and acrylates are compounds which are conventionally usedin the field under consideration. These compounds may optionally befluorinated. The diisocyanate can be replaced by a polyisocyanate, butfor convenience, the first term will be used as the generic term.Examples of such diisocyanates, acrylates, and vinyl ethers can be foundamongst the compounds cited in EP-A-0 565 425, including fluorinatedcompounds (as long as they contain no sulfur), and amongst the compoundscited in French patent application FR-A-2 712 291.

To prepare fiber coatings, the material of the invention, which also hasthe particular feature of being curable, is light-cured, in general byUV, preferably in the presence of a reactive diluent which is generallya diacrylate, present in a conventional amount.

Conventionally, photoinitiators and/or catalysts are used for the(photo) chemical reactions, if necessary.

The fluorinated diols used in the invention are novel.

The fluorinated diols of the invention, where R is C₂H₅, are prepared byradical reaction of C_(n)F_(2n+1)I with allyloxy trimethylol propane (ortrimethylol propane monoallylether) followed either by dehydroiodationoptionally followed by hydrogenaton, or direct reduction orhydrogenolysis.

While the description has been made with reference to the diol where Ris C₂H₅, clearly other compounds are prepared in the same mannerstarting from the appropriate monoallylether. This monoallyl ether isthe trimethylol alkane monoallylether, with the alkane corresponding tothe group R increased by one carbon atom.

Radical addition can be carried out using known operating procedures,either in the solid state, or in an organic solvent, or in water.

Such radical addition has been described in German patent applicationDE-A-2 336 913, the reaction conditions of which can be followed.

The organic solvent can be acetone, tetrahydrofuran, dioxane,dimethylformamide, N-methyl-2-pyrrolidone, dimethylsulfoxide, methylethyl ketone, methyl isobutyl ketone, ethanol, isopropanol, or isopropylacetate. Preferably, a hydrosoluble solvent or a mixture of hydrosolublesolvents is used.

Radical addition is normally carried out in the presence of initiator(s)which are used in an amount of 0.1% to 1.5% with respect to the totalweight of the monomers used, preferably 0.1% to 0.5%. The initiators canbe peroxides such as benzoyl peroxide, lauroyl peroxide, succinylperoxide, or tert-butyl perpivalate, or azo compounds such as2,2′-azobisisobutyronitrile, 4,4′-azobis(4-cyanopentanoic acid), and2,2′-azobis-[2-methylbutanenitrile].

The reaction temperature range is wide, i.e., from ambient temperatureto the boiling point of the reaction mixture. Preferably, a temperatureof 60° C. to 90° C. is used; (thus avoiding polymer formation).Similarly, the allyloxy trimethylol propane can be added dropwise tocontrol the reaction and limit the temperature rise.

An iodine-containing addition product is thus obtained.

Dehydroiodation is carried out using a strong inorganic base such assodium or potassium hydroxide, or a strong organic base such as DBU(1.8-diazabicyclo(5.4.0)undec-7-ene). The reaction is preferably carriedout in an aqueous medium. By way of example, the quantity of strong baseused is close to the stoichiometric amount. The temperature is generallylimited to about 70°-75° C. (thus avoiding polymer formation).

This produces an unsaturated diol.

Saturated diols can be produced by different methods. They can beobtained from an addition product iodized by hydrogenolysis in thepresence of an alkaline agent, or by reaction with sodium or zincborohydride or lithium aluminum hydride or tributyl tin hydride. Theycan also be obtained from an unsaturated derivative by catalytichydrogenation using known methods, either solvent-free or in solution ina conventional organic solvent such as ethanol or methanol, in thepresence of a hydrogenation catalyst which, depending on the case, canbe either Raney nickel or palladium on charcoal.

A saturated diol is thus obtained.

The perfluoroalkyl group C_(n)F_(2n+1) can be linear or branched. Thecompound C_(n)F_(2n+1)I is known per se and is prepared usingconventional methods.

The following examples illustrate the invention without limiting itsscope.

EXAMPLE 1

a) C_(n)F_(2n+1)—CH₂CHI—CH₂OCH₂—C(CH₂OH)₂C₂H₅: 125 grams weight of amixture of perfluoroalkyl iodides with formula: C_(n)F_(2n+1)I where nis 6, 8, 10, 12 and 14 in respective weight ratios of 63:25:8:2:2 (0.25mole) in solution in 200 grams of acetone and 64.5 grams of trimethylolpropane monoallylether (0.375 mole) were introduced into a one literreactor heated by a double thermostatted envelope provided with ananchor blade agitator and a refluxing coolant. After inerting withnitrogen and heating to 62° C., radical addition was initiated with 0.4gram of azobis-isobutyronitrile (AIBN) then 0.2 grams of AIBN was addedevery 2 hours. The C_(n)F_(2n+1)I perfluoroalkyl iodide conversion wasmonitored by gas chromatography. The reaction was complete after 20hours. After evaporating off the acetone under reduced pressure, thereaction mass was washed three times with 200 grams of demineralizedwater at 60° C. to eliminate the excess trimethylolpropanemonoallylether. The addition product, in the form of a pale yellowviscous liquid, was separated by decanting then vacuum dried. Itcrystallized slowly at ambient temperature and had a melting point ofabout 41° C. The yield with respect to the C_(n)F_(2n+1)I waspractically quantitative.

b) C_(n)F_(2n+1)—CH═CH—CH₂OCH₂—C(CH₂OH)₂—C₂H₅: Using the same reactor,the same reaction was carried out using identical quantities. Afterdecanting, the aqueous washing phase was removed by aspiration then theaddition product obtained was dehydroiodated without being isolated. Tothis end, it was maintained at 50° C. and an aqueous sodium hydroxidesolution, i.e., 10.7 grams of sodium hydroxide (0.27 mole) in 50 gramsof water, was added dropwise over one hour, so as not to exceed 65° C.The iodine-containing derivative conversion was monitored by gaschromatography: it was complete after 7 hours. After decanting, theaqueous phase was eliminated by aspiration then the organic phase waswashed with demineralized water at 50° C. to neutrality. Afterseparating the aqueous phase, the fluorinated diol obtained was dried byazeotropic distillation with cyclohexane. The solvent was then distilledunder reduced pressure. A pale yellow viscous liquid was obtained in ayield of 95% with respect to the starting C_(n)F_(2n+1)I.

EXAMPLE 2

The procedure of Example 1 was followed, replacing the C_(n)F_(2n+1)Imixture with C₆F₁₃I. The experimental conditions were the same and theiodine-containing addition compound was obtained quantitatively in theform of a pale yellow solid with a melting point of 46° C.

The structure was confirmed by proton NMR (300 MHz, CDCl₃). The chemicalshifts δ were as follows:

4.42 ppm (—CH—I, quintuplet, 1H);

3.60-3.80 ppm (—CH₂—OH, complex group of peaks, 4H);

3.54 ppm (—OCH₂—C, singlet, 2H);

2.60-3.05 ppm (—CH₂CF₂—, complex group of peaks, 2H);

1.35 ppm (CH₂CH₃ quadruplet, 2H);

0.86 ppm (CH₂CH₃, triplet, 3H).

After dehydroiodation under the conditions described for Example 1b), apale yellow viscous liquid (v≈1300 cps) was obtained with a density of1.43. It was a mixture containing 1.3 mole % of starting diol, 73 mole %of trans isomer, 25 mole % of the cis isomer of the unsaturatedfluorinated diol. Proton NMR analysis (400 MHz, CDCl₃) gave thefollowing signals:

Trans isomer:

6.45 ppm (CF₂—CH_(A)═CH_(B), D*T*t, ³J_(HA-F)=4.2 Hz, ³JH_(A)−H_(B)=15.8Hz, 1H);

5.90 ppm (CH_(A)═CH_(B)—CH₂—O, D*T*t, ⁴J_(HB-F)=12 Hz, 1H);

4.15 ppm (═CH—CH₂O, complex group of peaks, 2H)

3.55-3.75 ppm (CH₂OH), complex group of peaks, 4H);

3.50 ppm (O—CH₂—C, singlet 2H);

1.34 ppm (CH₂—CH₃, quadruplet, 2H);

0.85 ppm (—CH₂—CH₃, triplet, 3H)

Cis isomer:

6.25 ppm (CF₂—CH_(A)═CH_(B), D*T*t, ³J_(HA-F)=2.5 Hz, ³J_(HA)−H_(B)=12.5Hz, 1H);

5.60 ppm (CH_(A)═CH_(B)—CH₂—O, D*T*t ⁴J_(HB-F)=15.5 Hz, 1H);

4.28 ppm (═CH—CH₂O, complex group of peaks, 2H);

3.55-3.75 ppm (CH₂—OH, complex group of peaks, 4H)

3.44 ppm (O—CH₂—C, singlet, 2H);

1.34 ppm (—CH₂—CH₃, quadruplet, 2H);

0.85 ppm (—CH₂—CH₃, triplet, 3H)

EXAMPLE 3

a) 273 grams of perfluoroalkyl iodide C₈F₁₇—I (1.5 mole) previouslywashed at ambient temperature with an aqueous bisulfite solution toeliminate traces of iodine-containing impurities, 93 grams oftrimethylolpropane monoallylether (0.53 mole) and 120 grams ofdemineralized water were introduced into a 1 liter reactor heated by athermostatted double envelope and provided with an anchor blade agitatorand a reflux coolant. The heterogeneous mixture was inerted withnitrogen then heated with vigorous stirring at 70° C. 0.4 grams of AIBNinitiator was then added. The reaction was exothermic and the doubleenvelope was cooled for several minutes so as not to exceed 90° C. Thetemperature was kept at 75° C. and the reactant conversion was monitoredby gas chromatography. 0.2 grams of AIBN was added every two hours.C₈F₁₇—I conversion was complete after 6 hours. The excess starting diolwas eliminated by washing the organic phase three times with water at75° C. Analyzing the latter confirmed the presence of the expectedaddition product as the major compound. This intermediate rapidlysolidified (72° C.).

b) In the same reactor, the dehydroiodation reaction was commenced,directly on the organic phase. This latter was kept at 70° C. and 60grams of water was added at 60° C., then a solution containing 20.3grams of sodium hydroxide (0.5 mole) in 80 grams of water was addeddropwise over one hour so as not to exceed 60° C. After 6 hours, GCanalysis showed that the reaction was complete. After decanting, theaqueous phase was eliminated by aspiration then the organic phase waswashed with demineralized water at 50° C. to neutrality. Afterseparating out the aqueous phase, the fluorinated diol obtained wasdried by azeotropic distillation with cyclohexane. The solvent was thendistilled off under reduced pressure. A pale yellow viscous liquid wasobtained which slowly solidified at ambient temperature (MP=38° C.) witha yield of 95% with respect to the starting C₈F₁₇—I. It was a mixturecontaining 0.7 mole % of starting diol, 73.1 mole % of trans isomer and24.5 mole % of cis isomer.

Carbon-13 NMR analysis (75.5 MHz, CDCl₃) produced:

the following signals for the trans isomer:

138.8 ppm (CF₂—CH═CH—, ³J_(C-F)=9 Hz);

117.3 ppm (CF₂—CH═CH, ²J_(C-F)=23.7 Hz);

73.4 ppm (CH₂O—CH₂—C—);

69.6 ppm (═CH—CH₂—O);

66.1 ppm (—CH₂OH);

43 ppm (C(CH₂OH)₂);

23.0 ppm (CH₃—CH₂—);

7.4 ppm (CH₃—CH₂—);

the following signals for the cis isomer:

142.3 ppm (CF₂—CH═CH—, ³J_(C-F)=5.6 Hz);

117 ppm (CF₂—CH═CH, ²J_(C-F)=23.7 Hz);

73.8 ppm (CH₂O—CH₂—C—);

67.5 ppm (═CH—CH₂—O);

66.0 ppm (—CH₂OH);

42.9 ppm (C(CH₂OH)₂);

23.0 ppm (CH₃—CH₂—);

7.4 ppm (CH₃—CH₂—);

EXAMPLE 4 C₆F₁₅—(CH₂)₃OCH₂—C(CH₂OH)₂C₂H₅

492 grams (1 mole) of the C₆F₁₃ fluorinated diol described in Example 2in 370 grams of methanol and 20 grams of 5% palladium on charcoal and 10grams of K₂CO₃ were introduced into a stirred reactor with a volume ofabout 1 liter. Hydrogen was added to a pressure of 20 bars. The reactionwas exothermic: the temperature rose to 50° C. while the pressure fellto 5 bars over 10 min. Hydrogen was added again to a pressure of 20 barsuntil no more hydrogen was absorbed. The reaction was ended at 40° C. at60 bars. Gas chromatographic analysis showed that all of the unsaturateddiol had been transformed. The catalyst was separated by filtering, thenthe solvent was eliminated under reduced pressure. The structure of thesaturated diol obtained in a yield of 97° C. was confirmed by proton NMR(400 MHz, CDCl₃):

The following was observed:

the signals at 6.45 and 6.25 ppm (CF₂—CH_(A)═CH_(B)) of the cis/transisomers disappeared;

the signals at 5.90 and 5.60 ppm (CH_(A)═CH_(B)—CH₂—O) of the cis/transisomers disappeared;

3.5 ppm (—CH₂—CH₂O, triplet);

3.6-3.7 ppm (CH₂OH, complex group of peaks, 4H);

3.44 ppm (O—CH₂—C, singlet, 2H);

2.15 ppm (CF₂—CH₂, broad multiplet);

1.89 ppm (CF₂—CH₂—CH₂—, broad multiplet);

1.34 ppm (—CH₂—CH₃, quadruplet, 2H);

0.85 ppm (—CH₂—CH₃, triplet, 3H).

EXAMPLE 5

62 grams (0.1 mole) of the C₆F₁₃ iodine addition product described inExample 2, 13.8 grams (0.11 mole) of finely powdered potassiumcarbonate, 160 grams of absolute ethanol and 6 grams of 5% palladiumcatalyst on charcoal were introduced into a stirred autoclave with acapacity of about 0.5 liters. After purging with nitrogen, hydrogen wasadded to a pressure of 50 bars. It was heated to 60° C. with stirring.The pressure stabilized at about 40 bars after 20 hours. The catalystand carbonate were separated by filtering, then the solvent waseliminated under reduced pressure. The viscous liquid obtained wasre-dissolved in 200 ml of methylene chloride. The organic phase waswashed with water to eliminate KI, then dried over sodium sulfate. Afterfiltering then eliminating the solvent, the viscous liquid obtained,which solidified rapidly, contained no more iodine-containing additionproduct (analysis by gas chromatography). 47 g (i.e., a yield of 95%) ofthe same product as Example 4 was obtained.

EXAMPLE 6

The procedure of Example 4 was followed, replacing the C₆F₁₃ diol withthe C₈F₁₇ diol obtained in Example 3. Under identical conditions, thesaturated solid fluorinated diol was obtained in a yield of 96%.

EXAMPLE 7

610 g of 2,2,4-trimethyl-hexamethylene diisocyanate and 26.5 g ofdibutyl dilaurate tin were introduced into a 5 liter reactor. 715 g ofthe fluorinated diol of Example 2 was added, and the mixture was allowedto react for 1 hour at 80° C. The temperature was allowed to fall to 40°C., then 2.9 g of ionol, 492.7 g of hexamethylene diacrylate and 343.8 gof 2-hydroxyethylacrylate were added. The reaction was allowed tocontinue until infrared analysis showed that the isocyanate band at 2260cm⁻¹ had disappeared. 5% by weight of Irgacure 184 photoinitiator wasthen added.

A fiber was then coated whereby the primary coating was a standardcoating and the secondary coating was a coating of the material producedabove. Photopolymerization was carried out under UV.

The static fatigue was then measured with two points of flexion. Fibers2.5 cm in length were washed in precision glass tubes; 20 fibers wereplaced in each tube. 5 tubes with different diameters were used,imposing the following stresses on the fibers:

1. 456 kpsi (3144 MPa);

2. 419 kpsi (2889 MPa);

3. 399 kpsi (2751 MPa);

4. 386 kpsi (2661 MPa);

5. 353 kpsi (2434 MPa).

The stressed fibers were placed in a climatized chamber at 85° C., with85% relative humidity. The rupture time for each fiber was automaticallyrecorded via an acoustic detector. The time to rupture was plotted as afunction of the applied stress on a logarithmic scale and the staticfatigue factor n was calculated from the slope of the straight lineobtained. In the case of a standard coating, the value of n was 18-20,while with the fluorinated diol-based composition of the invention, thevalue of n was 23.

The invention is not limited to the embodiments described; it can, forexample, be applied to fiber ribbons. The fluorinated diol can also beused as a mixture with other diols. The diisocyanate can be completelyor partially replaced by a polyisocyanate.

What is claimed is:
 1. A polyurethane polymeric material for coatingoptical fibers, based on at least one diol, a diisocyanate and anethylenically unsaturated compound, characterized in that the diol is afluorinated diol with formula I: C_(n)F_(2n+1)—A—CH₂OCH₂—C(CH₂OH)₂—Rwhere n is 2 to 20, and A signifies —CH═CH or —CH₂CH₂—, and R is analkyl group containing 1 to 4 carbon atoms.
 2. A polymeric materialaccording to claim 1, in which the diol is unsaturated and correspondsto formula: C_(n)F_(2n+1)—CH═CH—CH₂OCH₂—C(CH₂OH)₂—C₂H₅.
 3. A polymericmaterial according to claim 1, in which the diol is saturated andcorresponds to formula: C_(n)F_(2n+1)—CH₂CH₂—CH₂OCH₂—C(CH₂OH)₂—C₂H₅. 4.A polymeric material according to claim 1, in which in the diol, R isC₂H₅.
 5. A polymeric material according to claim 1, in which in formula(I), n is a whole number and is in the range 6 to 14 inclusive.
 6. Apolymeric material according to claim 1, in which in formula (I),C_(n)F_(2n+1) results from a mixture and n is in the range 6 to 14inclusive.
 7. A polymeric material according to claim 1, in which informula (I), n is in the range 6 to 8 inclusive.
 8. A polymeric materialaccording to claim 1, in which the ethylenically unsaturated compound isan acrylate.
 9. A method of preparing a material according to claim 1,comprising: (i) a step of reacting the fluorinated diol with thediisocyanate to produce a fluorinated diisocyanate pre-polymer; (ii) astep of reacting the fluorinated diisocyanate pre-polymer with ahydroxyl-containing ethylenically unsaturated compound.
 10. A fibercoated with at least one coating of a material according to claim 1which has been light-cured.
 11. A fiber according to claim 10, in whichthe material is light-cured in the presence of a diacrylate as areactive diluent.
 12. A fiber according to claim 10, in which thecoating is the secondary coating.
 13. A fiber drawing method, comprisinga step of coating the fiber with a material according to claim 1,optionally as a mixture with a diacrylate as a reactive diluent, andincluding a step of light-curing.
 14. A polymeric material according toclaim 1, wherein the polymeric material is free of sulfur.